The manufacture of semiconductors can involve a variety of unit processes including physical vapor deposition, metal and dielectric chemical vapor deposition, plasma etching, chemical-mechanical polishing and the like. Any or all of these units may be located in a single fabrication facility. These fabrication facilities include clean room facilities in which the various unit processes are located in order to reduce particulate contamination that can cause defects in the wafer. Because it is expensive to build and operate clean rooms, only those portions of the process that are associated directly with the wafer are housed in the clean room. Presently, fabrication facilities have different levels of clean room environments so that the most sensitive processes or procedures can be carried out in the most clean environments and the most insensitive processes or procedures can be carried out in less clean environments. In this manner, the use of the most expensive space is minimized.
Furthermore, it is generally desirable to minimize the use of materials and equipment in the clean room that can generate particles and release them into the air. Therefore, materials that out gas contaminants or generate particles are kept outside of the clean room area that houses sensitive processes. Likewise, equipment that emits byproduct gases, generates particles, alters the humidity or suffers occasional spills are kept in remote locations outside of clean room areas.
While each process has distinctive characteristics and may require specific accommodations for installation and operation, there are some aspects of their operation that are similar. For example, many semiconductor processes are carried out under specific conditions, such as temperature and pressure. These temperatures and pressures may vary between processes and may even vary within the same process over time or according to the particular process recipes being performed.
Temperature control of processing conditions may be used beneficially for many purposes. For example, temperature control of the substrate receiving surface of a support member can enhance uniformity and deposition rate on the substrate. Temperature control of the processing apparatus side walls can also enhance such processing by reducing undesirable condensation of chemical vapors on the chamber walls. Cooling of wafers following certain warm deposition processes speeds the solidification of the deposited materials prior to additional processing and reduces out gassing of undesirable and often corrosive gases when the wafer is removed from the cluster tool.
In those applications, such as temperature control of chamber walls, where a heat transfer fluid may be used to heat or cool a processing unit or chamber component, the fluid is circulated through a heat exchanger which is controlled to deliver the fluid at the temperature desired of the chamber component. For example, if a given substrate is to be processed in a manner that calls for a chamber wall temperature of 150.degree. C., the heat exchanger provides sufficient heat to the circulating fluid so that the fluid temperature leaving the heat exchanger is about 150.degree. C. The setpoint temperature of the exchanger output may be increased to account for an average temperature drop through the tubing and chamber wall. However, this type of adjustment does not allow the temperature of the chamber wall to be maintained under changing thermal loads associated with substrate processing. Separate, dedicated heat exchangers have been required to provide for independent fluid temperatures at different processing units.
A strong need exists for a system that can control the temperature of semiconductor processing chambers despite changes in the thermal loads associated with substrate processing. There is also a need for a temperature control system that involves fewer parts and can rapidly and effectively change the surface temperature of a process element. The system should possess the ability to reduce thermal losses and thermal lag. It would also be desirable if the system provided independent control for each process component.